I'm looking for some suggestions or insight into a recent problem. This may be a long post ... grab a beer and read on.
First the facts. In early September, two things began happening with my GTM at the exact same time:
When I depressed the clutch pedal just a tiny bit, I could hear a tic-tic-tic sound coming from the transaxle. I could also feel a very slight pulsing in the clutch pedal. When I depressed the clutch pedal more fully, the tic-tic-tic sound lessened a bit, and the pulsing lessened as well. The clutch and transmission still operated as intended.
The engine cuts out when I decelerate in gear, foot off the gas completely, then depress the clutch. Feels like it simply turns off as the RPMs fall below 1000. No codes. When this happens, its often very difficult to start the engine again. However, if I depress the clutch first and then let off gas I come to a perfect idle with no problem whatsoever.
Both of these issues started at the exact same time and so I'm thinking somehow must be related. First 3500 miles were perfect.
I have a stock crate LS3 with GMPP ECU.
To figure this out, I removed the transaxle and clutch this past weekend (thanks for the help Ron) to see what I could see.
The wear surfaces of the clutch, flywheel and pressure plate looked just fine. No broken springs in the clutch. No readily apparent problem.
Then I looked a little closer and I think I found the problem. Inside the transaxle bell housing there is a boss that protrudes toward the pressure plate, almost directly above where the opening in the housing is for the pivot shaft. On my transaxle, this boss has been ground down a bit and shows fresh wear. Something is grinding it. See photos 1, 2, 3 below.
On my pressure plate, I noticed that two of the "pins" along the outer rim also show signs of fresh wear. These two pins protrude much farther than all the others. See photos 4, 5 below.
I'm guessing that as I depress the clutch pedal and the clutch fork begins to pull on the throwout bearing, the pressure plate is moving just enough for the pins to contact the boss and grind, hence the tic-tic-tic as the pressure plate spins. Heck, for all I know it's grinding on the boss all the time.
So obviously I have a grinding issue, but why did it start after 3500 miles? I have no idea if I have excessive play in the throwout bearing, but I'm taking it to a porsche shop tomorrow to have a look.
I'm thinking it would be easy to grind the boss down another few millimeters, as I can't imagine it serves any real purpose. But what caused this, and what is the correct fix?
If this was an old style small block I would suggest checking the thrust on the crank. I don't know much about te LS motors, Yet. Could this also cause a lost signal from the reluctor?? could be the cause of the killed engine. I hope not but sounds possible.
Scott
Last edited by scottvette1989; 01-05-2015 at 12:50 PM.
Reason: added thought
If this was an old style small block I would suggest checking the thrust on the crank. I don't know much about te LS motors, Yet. Could this also cause a lost signal from the reluctor?? could be the cause of the killed engine. I hope not but sounds possible.
Scott,
Thanks for the ideas. I've pieced some of the puzzle together, and I think you're probably correct. I'm going to measure the thrust on the crank this weekend. Once I have it all figured out I'll let everyone know what happened. Worst case is get a new pressure plate, pull the engine, replace the thrust bearings (only $32 but a pain in the a$$ to get to - nothing like a little bottom end engine work for a cold winter day), reinstall engine, reinstall clutch and transaxle, and hook everything else back up that needed to be undone to get it all out.
Too bad I'm not John (Kabacj) - all that would take him about 1 hour . Me, it will take 1 month . Can't drive anyway - too much ice on the roads!
Ha that's funny Michael. When you have pulled the motor/ transaxle in and out as many times as I have you get faster every time.
Sorry to hear about your problem. As you say it's too cold and icy to drive anyway, so now is a good time to get everything sorted.
At least checking the thrust bearing clearance is easy. I know from the two transaxle configurations I have used that the expected tolerances can be closer than any provider of components expects. Even a little wear could remove the small tolerances you had?
in your case, those little pins on the pressure plate might be just enough to cause an issue as it sounds like other pressure plate configurations are flush in that area.
At any rate I am hoping you have a quick and easy fix.
John
XTF #2
build start date June 19 2023
GTM # 344
Build Start December 2010
First track day April 2013
I'd guess that the 'pins' on the rim of the clutch are balance weights. You might be able to get scientific with removing them and drilling the other side to maintain the balance. (It wouldn't be balanced exactly the same, but clutches and flywheels usually have more static imbalance than couple imbalance.) Cutting down the boss on the transaxle sounds easier as long as it isn't there for a purpose. Either way, I'd try to get an 1/8" of clearance in there - sometimes stuff moves/flexes/vibrates more than we would want it to.
I'm pretty certain I have it figured out. Here's what happened (and what you all need to check to make certain it doesn't happen to you!). There were two contributing factors:
1. I had the wrong pressure plate. It should have been a Porsche pressure plate, but for some reason I had a KEP pressure plate. The KEP plates have the big balancing pins, the Porsche plates do not. The pins aren't the problem though. The problem is that this pressure plate requires more force to be applied to the throw-out bearing to release the clutch than would be required with a conventional Porsche pressure plate. When you push the clutch pedal, the force on the throw-out bearing pulls it toward the rear of the car to release the clutch. This pull is transmitted directly to the crankshaft, and the crankshaft thrust bearing counteracts this force to keep the crank in place. The bearing faces of the thrust bearing are rated for a only few hundred pounds of force. Bottom line, the thrust bearing cannot withstand much axial load - and the clutch system is capable of overloading the thrust bearing, especially if you use the wrong pressure plate!
2. I was an idiot an never put in a clutch stop. I was under the impression you needed a clutch stop to limit travel of the clutch fork so it didn't hit anything. When I installed my clutch I measured all clearances and had no issues, so I never installed the clutch stop. BUT THAT IS NOT WHY YOU INSTALL A CLUTCH STOP! You install a clutch stop to limit the force applied to the crankshaft thrust bearing! You want to adjust the clutch stop so the pedal travels 1/4"-1/2" past full clutch release. Any more motion than that only serves to put added stress on the crankshaft thrust bearing.
Taking these two things together leads to a failed thrust bearing at only 3500 miles. I measured my crank play and have nearly 0.065" - spec is less than 0.005". And when my clutch is fully depressed, it can move the crankshaft enough that the crank position sensor no longer lines up with the reluctor wheel and so I lose the signal and the engine shuts down. I believe I started hearing the tic-tic-tic when the thrust bearing failed, allowing the crankshaft/flywheel/pressure plate to be pulled backwards into to transmission housing, and the balancing pins started to hit the boss inside the housing.
So I spent this weekend preparing to remove my engine, so that I can replace my thrust bearing. Hopefully the crankshaft thrust surfaces are not damaged, but I won't know until I get in there and look. I've removed the rear hatch, cold air intake, exhaust, headers, wiring harness, intake manifold, and valley cover, and replaced the valley cover with an engine hoist plate. Also drained the oil and coolant, and removed the idler pulley assembly so I can lift the engine up and out without removing the rear wall. And removed the flywheel and KEP adapter plate. The engine looks downright naked!
The only thing remaining attached to the engine are the AC compressor and AC hoses. I'd like to remove the compressor/hoses together from the engine so that I don't have to recharge the AC system, but it looks very challenging to remove the compressor in the engine bay. If I do have to take the hoses off, do I just remove the aluminum hose manifold from the rear of the compressor and let the refrigerant escape into my shop? Not really certain what to do here.
As soon as I figure out how to handle the AC I'll pull the engine. Maybe tomorrow or Monday.
Unbolt the pump and let it stay there, take out the motor with the pump laying there and still hooked to the hoses.
Things are different now, but yes we used to let them bleed out into the air, people are worried about ozone now.
If you have to break it loose.
Thanks Gene. I was able to remove the bolts from the block so I'll be able to leave the compressor connected to the rest of the A/C system when I pull the engine.
How could you tell it was coming from the engine and not the trans? I ask as I occasionally get a ticking but it sounds like a lifter.
It was coming from the transmission ... the tic-tic-tic was the sound of the pressure plate bolt hitting a boss inside the bell housing. And I could feel the slight pulse in the clutch pedal each time I heard the tic sound. When you feel it in your foot and hear it at the same time, as you very slightly depress the clutch, you figure it's the transmission and not the engine. In fact, with the transmission engaged and driving I rarely heard the sound at all. But touch that clutch pedal, and tic-tic-tic!
I don't think there was anything to hear in the engine, even with the thrust bearing shot.
As I know I have stated on other threads involving clutch issues...EVERY CAR SHOULD HAVE AN ADJUSTABLE CLUTCH STOP. OEM street cars many times do not, but that is because every part is engineered as a system and safety margins are built into that system. When you start "upgrading" or mixing and matching parts, then you MUST HAVE A WAY OF LIMITING TRAVEL. To not do so will lead to problems such as this and others, like ruined pressure plates and broken transaxle castings.
That said, I really have a tough time believing you could build enough force to cause the thrust bearing issue with the force of the clutch hydraulic system. I don't think the pressure plate fingers are capable of transmitting that much force to the crank. They would severely fail first.
Again, if your engine came from a wrecked vehicle I think it is much more likely that whatever impact caused the vehicle to be totaled was probably to blame for the crank play issue.
Unbolt the pump and let it stay there, take out the motor with the pump laying there and still hooked to the hoses.
Things are different now, but yes we used to let them bleed out into the air, people are worried about ozone now.
If you have to break it loose.
Do NOT ABSOLUTELY NOT let the coolant loose in your garage!!!!!!!!!!!!
This has nothing to do with ozone...when the new coolants combine with any source of flame, or even heat, they produce phosgene, aka mustard gas, which is deadly at concentrations over 50 ppm.
The coolants are heavier than air, and will hang around in your garage for a while, too.
As I know I have stated on other threads involving clutch issues...EVERY CAR SHOULD HAVE AN ADJUSTABLE CLUTCH STOP. OEM street cars many times do not, but that is because every part is engineered as a system and safety margins are built into that system. When you start "upgrading" or mixing and matching parts, then you MUST HAVE A WAY OF LIMITING TRAVEL. To not do so will lead to problems such as this and others, like ruined pressure plates and broken transaxle castings.
That said, I really have a tough time believing you could build enough force to cause the thrust bearing issue with the force of the clutch hydraulic system. I don't think the pressure plate fingers are capable of transmitting that much force to the crank. They would severely fail first.
Again, if your engine came from a wrecked vehicle I think it is much more likely that whatever impact caused the vehicle to be totaled was probably to blame for the crank play issue.
Crash - I've heard you preach before and didn't appreciate the importance of those words. Woe unto me who did not listen!
As for the engine, it was a brand new crate LS3 broken in per the manufacturers directions. I'm amazed that the thrust bearing failed as well, and still won't be certain until I get engine out of the car, but I do have 1/16" of crank play, which is about 10x more than spec.
Do NOT ABSOLUTELY NOT let the coolant loose in your garage!!!!!!!!!!!!
This has nothing to do with ozone...when the new coolants combine with any source of flame, or even heat, they produce phosgene, aka mustard gas, which is deadly at concentrations over 50 ppm.
The coolants are heavier than air, and will hang around in your garage for a while, too.
Thanks Taz- No worries. I was able to unbolt the compressor from the block and keep the Ac system intact.
It was coming from the transmission ... the tic-tic-tic was the sound of the pressure plate bolt hitting a boss inside the bell housing. And I could feel the slight pulse in the clutch pedal each time I heard the tic sound. When you feel it in your foot and hear it at the same time, as you very slightly depress the clutch, you figure it's the transmission and not the engine. In fact, with the transmission engaged and driving I rarely heard the sound at all. But touch that clutch pedal, and tic-tic-tic!
I don't think there was anything to hear in the engine, even with the thrust bearing shot.
-Michael
Thank you for the response. Not the sound I am hearing.
That's an interesting point on the refrigerants and phosgene gas. I never knew that. Seems a lot of people have been affected or even killed by that who work in the HVAC industry. Crazy stuff.
Folks - another long post, but worth the read (I hope).
Yesterday, with the help of Ron (Presto51), I pulled the engine out of my GTM so I could investigate the thrust bearing problem. Got the engine and mounted it on an engine stand, spun it bottom side up, removed the oil pan, oil pickup, and windage tray. And then I saw the extent of my problems.
The thrust bearing in the LS3 engine is in the #3 (center) bearing position. When you push the clutch pedal, the thrust bearing keeps the crankshaft from moving rearward. In our GTM application, the forward facing surface (wrt to the engine) of the thrust bearing is the load-bearing side when the clutch is depressed (the clutch pulls the crankshaft toward the rear of the engine). This load-side surface of the thrust bearing bears against the rearward-facing crankshaft thrust surface. All this is shown in the first picture below. When all is well with the thrust bearing and crankshaft thrust surfaces, the crankshaft can only move fore/aft a few thousandths of an inch. For the LS3 the spec is between 2-6 thousandths. Remember, mine was moving about 65 thousandths (1/16”).
To assess the thrust bearing, I removed the #3 main cap and took out the thrust bearing. The second picture below shows what I found. First of all, the load-side surface has worn about 30 thousandths compared to the no-load surface! The no-load bearing thickness measures 0.093”, while the worn side measures 0.062” thick. Second, the crankshaft thrust surface on the load side is deeply scored compared to the no-load side. This is shown in the second picture as well. A good crankshaft thrust surface is slightly raised off the crankshaft web and machined flat and smooth. On the load bearing side, my crankshaft thrust surface has actually lost about 40 thousandths of material, and is badly scored. And the crankshaft thrust surface cannot be re-machined. I need a new crank.
The large rearward movement of the crankshaft has also caused grinding between the front-facing side of my #2 Main Cap and the corresponding rear-facing side of the crankshaft web. These are not bearing surfaces and should never be in contact! Both surfaces are now grooved from wear. And the grinding here has also caused heating of the #2 Main Cap (and probably the block itself) as evidenced by the heat-affected zone discoloration on the top surface of the #2 Main Cap. All of this can be seen in the third picture.
Remember, I only have 3500 miles on this brand new crate engine, and have changed the oil three times so far. I never noticed any metal in the oil before, but when I dropped the pan this time it was clearly there. I cut open the oil filter to look at the unfiltered oil and it looked like I was looking at a metallic paint. Very, very fine metal particulate in the oil.
Fortunately, the normal bearing surfaces looked fine. The cylinder walls look new. And the camshaft looks good. Regardless, the entire engine will be disassembled, thoroughly cleaned, and rebuilt. At minimum a new crankshaft (probably forged) and main bearings will be required. Maybe more.
I also believe I know why I had trouble starting my hot engine. In the hot engine, everything expands because of the heat. The grinding between my #2 Main Cap and crankshaft web likely gets worse as the engine heats and expands, especially these two areas since they are never meant to make contact. For a hot engine start, these parts have expanded, and when I depress the clutch they are forced together. It’s a huge surface area with a lot of friction that I believe the starter motor simply cannot overcome. The engine doesn’t turn at all – it seems as if you have a dead battery. Let the engine cool, those parts shrink a bit, and even if there is only 0.001” clearance when cold, the engine can still turn, and starts fine. That also explains why it can still be roll-started.
Many people have mentioned the hot-start problem, and there have been many guesses why – electrical problem, fuel, etc., but no real solutions. All of the symptoms others have reported are the same as mine, and I wouldn’t be surprised if their thrust bearings had worn and they are having the exact same problem I am. I was fortunate enough that I had the wrong pressure plate and heard the tic-tic-tic. If I hadn’t, I may have done even more damage to the engine internals.
Bottom line – install the correct clutch. Definitely install a clutch stop. And save the cost of an engine rebuild.
That is great information Michael. Thanks for the detailed post. It seems very reasonable that the hot start problem was related to over driven clutches wearing the thrust bearings and an engine that was effectively applying the brakes to the starter.
Glad to hear you got to the bottom of your problem.
John
XTF #2
build start date June 19 2023
GTM # 344
Build Start December 2010
First track day April 2013
The other thing I can see substantially irritating this issue is turning the engine over without the required oil pressure and having the clutch depressed at the same time. Once you get this engine back together, you might want to make sure you bring oil pressure up by turning the engine over with the spark plugs removed and the clutch NOT depressed. Combined with a quality assembly lube, this will insure that the bearings get oil before any substantial loads are applied. These little details can be VERY important.
The clutch stop/info should be included with the kit in my opinion. Pretty big deal when it can ruin an engine. Hope you get it back together with no more problems.
Thrust bearing edge chamfered to allow pressurized oil to flow to the thrust surface
New Melling high volume oil pump
New ARP bolts all around
I reinstalled it in the GTM last month with the help of Ron (Presto51), and reinstalled the transmission with a new correct pressure plate. This time I did it without floss or tape holding the clutch fork in place. I simply placed the fork in the bell housing, and then jiggled it in place as we put the transaxle on. It was really easy. FYI.
I also fabricated a clutch stop and set it so the pedal has about 1/2" travel after the clutch releases. And have set the clutch pedal so there is a ton of dead space before the clutch disengages. I'm trying now for no, zero, nada, pressure on the crankshaft when the clutch is not depressed.
Shane - I also noted that the return spring in the slave cylinder does exert constant pressure on the clutch fork. I don't know if it's too much or not, but I'm going to look into that this winter.
After putting it all back together I brought it to the shop that rebuilt the engine and had the car tuned. I'm happy to say it now runs fine. I picked it up this morning and drove home (about 40 miles) with no problems. Just a bit more power and torque than when I dropped it off. The custom cam definitely gives it a more muscular, aggressive sound too .
The shop broke in the engine on their engine dyno before I installed it in the GTM. On the engine dyno she ran 550 max HP and 525 ft-lbs max torque. Once I installed the engine back in the GTM they tuned it on their chassis dyno and my rear wheel to-the-pavement numbers are 435 HP and 406 ft.-lbs torque. Very nice for a relatively mild-mannered LS3. I've attached my dyno plots as well. If you believe the numbers across two different dynos, that represents a 21% driveline loss.
Almost forgot - while the GTM was in repair for the last year I added two of Shane's products. The rear diffuser louvers, and the rear hatch props. Both look great.
So that's it for now. I'm happy to be back on the road just in time for winter.
Micheal, you resurrected this thread just in time for me. I'm about to install my transaxle this weekend or next and you reminded me of the importance of the clutch stop. If you have a pic of the one you fabbed up and installed could you post it?
Michael,
Lots of reasons for 21% drivetrain loss. Peak torque is at a much higher RPM on the engine dyno chart. Since I am sure the cam and heads were not changed, I am guessing they used a different exhaust or intake system for testing on the stand. Also you mentioned tuning in the car thus implying that the ECU was not pulled and tuned on the stand. Intake and/or exhaust change could easily up the normal 15%+- loss to 21%. Other factors could be cold transmission lube, tire pressure, brake pads not pushed back, and sweep rate. Changing the sweep rate will change indicated HP even when on the same dyno on back to back runs. Basically it takes some HP to accelerate the flywheel and other internal components. If you try to let the engine increase RPM at a high rate, say 1000 rpm/sec, it uses much of it's power just to accelerate itself. If you want to brag, just have them run a "step" test where the engine is held at each point for a second or so. The mags used to do that to show high numbers. 200 rpm/sec is a fairly typical sweep rate. Use lower for glory runs, higher for ease on the engine.
Torque and HP curves look great! Pulls strong to 6500rpm and beyond. It should be fun to drive.
Ken
Michael,
Lots of reasons for 21% drivetrain loss. Peak torque is at a much higher RPM on the engine dyno chart. Since I am sure the cam and heads were not changed, I am guessing they used a different exhaust or intake system for testing on the stand. Also you mentioned tuning in the car thus implying that the ECU was not pulled and tuned on the stand. Intake and/or exhaust change could easily up the normal 15%+- loss to 21%. Other factors could be cold transmission lube, tire pressure, brake pads not pushed back, and sweep rate. Changing the sweep rate will change indicated HP even when on the same dyno on back to back runs. Basically it takes some HP to accelerate the flywheel and other internal components. If you try to let the engine increase RPM at a high rate, say 1000 rpm/sec, it uses much of it's power just to accelerate itself. If you want to brag, just have them run a "step" test where the engine is held at each point for a second or so. The mags used to do that to show high numbers. 200 rpm/sec is a fairly typical sweep rate. Use lower for glory runs, higher for ease on the engine.
Torque and HP curves look great! Pulls strong to 6500rpm and beyond. It should be fun to drive.
Ken
I will try to post a pic of my clutch stop. Basically a hard (urethane) bump stop, a sleeve nut, and a short bolt. I drilled a hole in the plate that holds the master cylinders, inserted the bolt from the front and screwed on the sleeve nut and bump stop. I may have to shorten the sleeve nut if I get a smaller master cylinder that increases pedal travel.0101160002d.jpg
Ken